Abstract: Improved tungsten coil filaments having good sag resistance and useful in double ended, high intensity and energy efficient tungsten halogen lamps having an IR reflecting filter on the filament chamber. These coil filaments have a microstructure which is a large, elongated and interlocking grain structure produced by a high temperature heat treatment process.

Abstract: An improved inlead construction for an electric lamp is disclosed which utilizes an iron alloy containing sufficient silicon to avoid transformation of the inlead from the alpha ferrite phase to the gamma austenite phase at lamp operation temperatures. This precludes debilitating deformation of the inlead wires caused by on-off cycling of the lamp and concomitant cycling of the wire through the alpha to gamma transformation range. Such deformation can lead to structural or operational failure if the inleads become disconnected or electrically shorted from the resistive filament during lamp operation. In a preferred lamp construction, a pair of the improved inlead wires serve as the sole means of physical support for a resistive incandescent filament directly connected thereto and said inlead wires can further be coated with a dissimilar metal for higher lamp loading requirements in order to help avoid iron migration which can produce deterioration of the resistive incandescent filament.

Abstract: An electric lamp filament of tungsten is disclosed that has been coiled and heat-treated to at least 1600.degree. C. on a wire mandrel containing molybdenum but which is essentially free of molybdenum contamination. A barrier layer of tungsten or tantalum is provided on said mandrel to preclude the molybdenum contamination and the coated mandrel can thereafter be dissolved from the uncontaminated tungsten filament coil in an acid mixture.